Eneloops
I have four JR transmitters, 2 x 10x and 2 x 12x which I still use and which were changed to Eneloop 8 years ago.
prior to the new season I was checking them for capacity and internal resistance, and frankly, they checked out virtually as good as a new one which arrived today. Amazing.
However, one of the 10xs which had previously used NiCads had black wire syndrome on the negative cable between the battery and the little PC board in the battery housing.
So, as this is a potential killer, if you have a tx which has previously used NicAds, may be a good idea to take a look, the fix is quick and easy.